Embed Size (px)
DESCRIPTION
Introduction to NI Actor Framework. How to integrate DIM? DIMActor Ancestor Class. - PowerPoint PPT Presentation
Citation preview
Introduction to NI Actor Framework
How to integrate DIM?DIMActor Ancestor Class
DIMActor von Dr. Holger Brand steht unter einer Creative Commons Namensnennung - Nicht-kommerziell - Weitergabe unter gleichen Bedingungen 3.0 Unported Lizenz.Über diese Lizenz hinausgehende Erlaubnisse können Sie unter https://www.gsi.de/work/organisation/bereiche/personalrecht/patente_und_technologietransfer.htm erhalten
28.02.2013
Agenda
• Prerequisites• Motivation: Active objects• LVOOP
• Pros & Cons• Application• NI Actor Framework
• DIM• Example:
• DIMActor anchestor class• DIMActor derived classes
• DIMDemoServer• DIMDemoClient
• How to extend existing Actors?• References
28.02.2013
Prerequisites
• LabVIEW Basics 1 & 2• Project Explorer• Libraries• Dataflow concept
• Is knowledge about object oriented programming necessary?• No!• LabVIEW-Classes enables a developer to define his own data types,
that provide much more abilities than (strict) type-definitions.• Experience with conventional OO programming languages, e.g. C++
or Java, is maybe confusing.
28.02.2013
LabVIEW Dataflow
• No variables are existing in LabVIEW• There are data sources and data sinks!
• A priori it is not clear from where data is originating! E.g.:• From front panel controls in case of interactive mode.• From calling VI as parameter via connector pane.
• Local and global variables are not really variables with respect to common sense, but different places in memory which are copied by LabVIEW Runtime-Engine asynchronously. This can lead to unintentional race conditions.
• Copies of data are created at wire forks.• The compiler is responsible to maintain a minimum number of copies to be used.• Therefore LabVIEW is inherent thread-save!• LabVIEW provides several options to transport data safely with respect to data flow
without race conditions between different threads, VIs or loops.• Queues, Notifications, FGV optionally protected by Semaphore etc.
• That’s all true for LabVIEW Objects, too!
28.02.2013
Pros of LVOOP Classes(in comparison to type definitions)
• Encapsulation• Attribute data is always private. It can be changed by class methods only.• The internal data structure is hidden.• Access rights: Public, Protected, Private, Community (friend)
• Modularity• Each class has its own clearly defined responsibility.• The public interface should be well defined.
• It should be modified with very good reason, only!
• Eases testability.• Extensibility
• Derived classes extend the attributes and methods of their ancestor class.• Specialization
• Derived classes special the behavior of their ancestor class.• LabVIEW Objects behave exactly like other LabVIEW data types
• They are following the dataflow paradigm!
28.02.2013
LVOOP Cons - Solutions
• There are no real cons.• (Copy-) Constructors and Destructors are not existing.
• They are simply not necessary. • LabVIEW Objects behave the same as other LabVIEW data types.
• Attributes are always private.• They cannot be displayed or changed directly on the front panel.• XControls are the solution for this problem.
• XControls can also be used as probes.
• Polymorphic class-VIs are not supported.• Parameters could be implemented as derived class of a common ancestor class.• Parameters as Variant.
• Especially Variant-Attributes.
• Multiple inheritance is not supported.• An alternative is the Composition design pattern
• References to Objects• Dataflow: Single Element Sized Queue• Data Value Reference
• Danger of deadlocks
28.02.2013
LVOOP Application
Possible cases for the application of LVOOP classes:• Cluster or type definitions, which become potentially extended, can be replaced with classes.
• Derives classes add attributes to the ancestor class. • Replacement of data type dependent (e.g. Enumeration) Case-Structures by dynamic dispatching.
• Dependent of the objects class the correct corresponding Overwrite-VI is called.
• Beispiel: Queued State-Maschine
• Development of generic frameworks• The application layer uses base classes only.• Details are implemented in derived classes.• Actor Framework ..............................................
28.02.2013
NI Actor FrameworkCommunication Scheme – Local Queues
Launching Actors• Actors are derived classes of
Actor.lvclass• Caller-Enqueuer
is used by Actor to send messages to the Caller.
• Actor-Enqueueris used by Caller to send messages to the Actor.
Asynchronous Communication via Queue• Messages are derived classes of
Message.lvclass• Messages are calling public VIs of an
Actor.• Actor-Messages can be generated
automatically be using Tools>Actor Framework Message Maker.
28.02.2013
Linked Network Actor: https://decibel.ni.com/content/docs/DOC-24051is using a nested actor maintaining networkstreams.
Network Communication: DIM
• Originally developed at CERN (www.cern.ch/dim)• DIM provides
• Publisher-Subscriber Pattern• Command Pattern
• DIM connects heterogenous systems.• Various operating systems• Various programming languages
• LabVIEW-DIM-Interface is existing• http://wiki.gsi.de/cgi-bin/view/CSframework/LVDimInterface
28.02.2013
DIMActor – Project & Class Hierarchy
• DIMActor.lvlib contains• DIMActor.lvclass derived from Actor.lvclass• DIMActor Messages
• DIMActorDemo.lvlib contains• Server
• DIMDemoServer.lvclass derived from DIMActor.lvclass• Server Messages
• Client• DIMDemoClient.lvclass derived from DIMActor.lvclass• Client Messages
• Application: Test.vi
28.02.2013
DIMActor Demo Application
• Initialize Caller to Actor Queue• Initialize DIMDemoServer• Initialize two DIMDemoClients• Launch Actors
• Wait for Stop• Sent Stop-Messages• Report Error
28.02.2013
DIMActor – Overwrite VI‘s
28.02.2013
Actor Core.vi
Stop Core.viPre Launch Core.vi
Dynamic Dispatch-VI:CastByteArrayAndDispatchMsg.vi
DIMActor – Dynamic Dispatch VI
28.02.2013
Dynamic Dispatch-VI:CastByteArrayAndDispatchMsg.vi
Example DIMDemoServer.lvclass:CastByteArrayAndDispatchMsg.vi
DIMActor – Other VIs
28.02.2013
Add Command Start Serving
Add Service Update Service
Add Subscription Probe
Extending existing Actors to use DIM
• Inherit from DIMActor.lvclass instead of Actor.lvclass• Extend Actor Core.vi to add
• Commands• Services• Subscriptions
• Overwrite: CastByteArrayAndDispatchMsg.vi• For each Command and Subscription
• Typecast DIM byte-array to expected G data type• Send corresponding (already existing) Message to self.
• Publish Service data where necessary.
• Use CoreLib.CallProcess.vi to sendMessages to CS-Objects
28.02.2013
References
• LabVIEW Menu -> Help -> Search the LabVIEW Help... -> Contents -> Fundamentals -> LabVIEW Object-Oriented Programming
• LabVIEW Menu -> Help -> Find Examples -> Browse by Task -> Fundamentals -> Object-Oriented
• LabVIEW Object-Oriented Programming: The Decisions Behind the Design • LabVIEW Object-Oriented Programming FAQ• Applying Common OO Design Patterns to LabVIEW• Actor Framework• Measurement Abstraction and Model-View-Controller (MVC) Project with A
ctor Framework in LabVIEW • HGF Baseclass Library • Mobile Agent System• Thanks to Stephen Mercer for his contributions to web documents &
discussions
28.02.2013
